Molecular mechanisms that control cell growth and division enable bacteria and other microorganisms to maintain a narrow range of cell sizes within a population. While the control of cell size is ubiquitous in biology, the evolutionary benefit of maintaining a characteristic cell size is not understood in detail. In this talk, I will analyze the advantage of cell size control strategies in growing populations of bacteria. I will discuss how mortality can select for accurate cell size control, and derive an analytical expression for the optimal cell size. I will show that non-genetic heritability of cell size gives bacteria an evolutionary advantage by enabling selection to act on the distribution of cell sizes in a population to reduce mortality rates. These results will be discussed in the context of experimental measurements in bacteria and their implications for the evolution of size control mechanisms.